## THERMAL SCIENCE

International Scientific Journal

### HYBRID AL2O3-CU/WATER NANOFLUID FLOW AND HEAT TRANSFER OVER VERTICAL DOUBLE FORWARD-FACING STEP

**ABSTRACT**

Turbulent heat transfer and hybrid Al2O3-Cu-nanofluid over vertical double forward facing-step is numerically conducted. The k-ɛ standard model based on finite volume method in 2-D are applied to investigate the influences of Reynolds number, step height, volume fractions hybrid Al2O3-Cu-nanofluid on thermal performance. In this paper, different step heights for three cases of vertical double forward-facing step are adopted by five different of volume fractions of hybrid (Al2O3-Cu-water) nanofluid varied for 0.1, 0.33, 0.75, 1, and 2, while the Reynolds number different between 10000 to 40000 with temperature is constant. The main findings revealed that rise in local heat transfer coefficients with raised Reynolds number and maximum heat transfer coefficient was noticed at Re = 40000. Also rises in heat transfer coefficient detected with increased volume concentrations of hybrid (Al2O3-Cu-water) nanofluid and the maximum heat transfer coefficient found at hybrid Al2O3-Cu-water nanofluid of 2% in compared with others. It is also found that rise in surface heat transfer coefficient at 1st step-Case 2 was greater than at 1st step-Case 1 and 3 while was higher at 2nd step-Case 3. Average heat transfer coefficient with Reynolds number for all cases are presented in this paper and found that the maximum average heat transfer coefficient was at Case 2 compared with Case 1 and 3. Gradually increases in skin friction coefficient remarked at 1st and 2nd steps of the channel and drop in skin friction coefficient was obtained with increased of Reynolds number. Counter of velocity was presented to show the re-circulation regions at 1st and 2nd steps as clarified the enrichment in heat transfer rate. Furthermore, the counter of turbulence kinetic energy contour was displayed to provide demonstration for achieving thermal performance at second step for all cases.

**KEYWORDS**

PAPER SUBMITTED: 2020-11-30

PAPER REVISED: 2021-01-18

PAPER ACCEPTED: 2021-02-02

PUBLISHED ONLINE: 2021-03-13

**THERMAL SCIENCE** YEAR

**2021**, VOLUME

**25**, ISSUE

**Issue 5**, PAGES [3517 - 3529]

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